Dual input AC and DC power supply having a programmable DC output utilizing a secondary buck converter

ABSTRACT

A dual input AC/DC power converter ( 10 ) having dual inputs ( 12, 14 ) adapted to receive both an AC and DC input and provide a selectable DC voltage output ( 16 ) and a second DC output ( 18 ). The dual input AC/DC power converter ( 10 ) comprises a power converter circuit ( 20 ) having an AC-to-DC converter ( 22 ), a DC-to-DC booster converter ( 24 ), a feedback circuit ( 26 ), a filter circuit ( 25 ) and a DC-to-DC buck converter ( 28 ). Advantageously, the power converter ( 10 ) resolves many of system management problems associated with carrying all of the different interface components necessary to power a wide variety of mobile products from either an AC or DC power supply. In addition, the power converter ( 10 ) also advantageously includes dual output voltage terminals ( 16/18 ) to allow for multiple mobile devices of varying power requirements to be powered, simultaneously, by a single converter.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to and claims priority from commonlyassigned U.S. patent application Ser. No. 10/005,961 filed Dec. 3, 2001,the teachings of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention generally relates to the field of powerconverters, and more particularly to a dual input AC and DC toprogrammable DC output power converter.

BACKGROUND OF THE INVENTION

As the use of mobile electronic products, such as PC notebooks, PDAs,cellular telephones and the like, continues to increase, the need forlow cost, compact power supplies to power and recharge these productsalso continues to increase. Most manufacturers of mobile productstypically include plug-in power adapters along with these mobileproducts to help facilitate the power supply needs of their customers.

Today's power adapters are typically AC-to-DC, or DC-to-DC powerconverters which are configured to either step-up or step-down the DCvoltage input delivered to the mobile device. With AC-to-DC adapters,for example, users can power most mobile devices by simply plugging theadapter into a simple AC wall outlet commonly found in most homes oroffices. Similarly, when only DC input power is available, such as in anautomobile or airplane, users can still power their mobile devices bysimply using a standard, off-the-shelf DC-to-DC adapter. Normally, bothadapters are designed and tailored to provide a regulated DC outputvoltage, which typically range from between 5VDC to 30VDC depending onthe kind of mobile device being powered.

Although these power adapters conveniently provide direct power andrecharging capabilities, users are often required to carry separateadapters to provide power to each individual mobile device. This oftenmeans that users have to carry multiple adapters: one for an AC inputpower source, and another for a DC input power source, moreover, userstypically carry multiple adapters to power multiple devices. Thus, bycarrying more than one device at a time, users of mobile product usersare forced to carry more than one bulk power supply adapter.

Accordingly, there exists a need for a power converter that resolves thesystem management problems associated with carrying all of the differentpower supply components necessary to power a wide variety of mobile orportable devices. Moreover, such a power converter would advantageouslyencompass serving the power supply needs of several different mobiledevices, as it would supply a filtered and regulated DC output voltagein response to either an AC and DC input voltage. Moreover, by having apower convert or having multiple output terminals, users have theability of providing power to several mobile devices of varying powerrequirements, simultaneously, regardless of whether the input voltage isAC or DC.

SUMMARY OF THE INVENTION

The present invention achieves technical advantages as a power convertercapable of supplying dual DC output voltages derived from either an ACinput voltage or a DC input voltage. The power converter can beexternally programmable to cover a wide range of voltage and currentcombinations, suitable for a wide variety of mobile product offerings.Moreover, the power converter also resolves the management problemsassociated with having several different interface components necessaryto power a wide variety of mobile products. By having dual outputvoltage connections, mobile product users can simultaneously powermultiple mobile devices of varying power specifications.

In one preferred embodiment, the invention is a power converter having afirst circuit adapted to receive an AC input voltage and provide a firstprogrammable DC output voltage. The power converter includes a secondcircuit adapted to provide a second programmable DC output voltage inresponse to a DC input voltage. The power converter also includes athird circuit that, in response to receiving the first and second DCoutput voltages, generates a selectable DC output voltage at a firstoutput. Moreover, the third circuit generally comprises a feedbackcircuit and is adapted to interface with a removable program module.This programming module feature allows users of the power converter toselectively establish the voltage level of the DC output voltage. Thepower converter also includes a fourth circuit that is coupled to firstoutput. The fourth circuit provides a second DC output voltage as asecond output which is independent of, and substantially lower than theselectable DC output voltage.

In another embodiment, the invention is a method of generating at leasttwo independently selectable DC output voltages in response to an ACinput voltage or a DC input voltage. This method is achieved by the actof converting the received AC or DC input voltage to a firstprogrammable DC output voltage at a first output. The converting act isthen followed by a receiving act wherein the first DC output voltage isreceived by a converting circuit. The converting circuit initiates agenerating act generating a second DC output voltage that is independentof and substantially lower than the programmable DC output voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the invention and the specific embodiments will beunderstood by those of ordinary skill in the art by reference to thefollowing detailed description of preferred embodiments taken inconjunction with the drawings, in which:

FIG. 1A shows a block diagram of a dual input AC and DC power converterhaving dual DC voltage outputs in accordance with the present invention;

FIG. 1B shows an exploded view of the converter with the detachable buckcircuit;

FIGS. 2A-C shows a schematic diagram of the power converter circuit asillustrated in FIG. 1 in accordance with the present invention; and

FIG. 3 shows a detailed schematic diagram of a DC-to-DC buck convertercircuit in accordance with the present invention; and

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The numerous innovative teachings of the present applications will bedescribed with particular reference to the presently preferred exemplaryembodiments. However, it should be understood that this class ofembodiments provides only a few examples of the many advantageous usesand innovative teachings herein. In general, statements made in thespecification of the present application do not necessarily delimit anyof the various claimed inventions. Moreover, some statements may applyto some inventive features, but not to others.

There is shown in FIG. 1A a block diagram of a dual input AC/DC powerconverter 10 having dual programmable DC voltage outputs in accordancewith the present invention. Preferably, the dual input AC/DC powerconverter 10 comprises a power converter circuit 20 having an AC-to-DCconverter 22, a DC-to-DC booster converter 24, a feedback circuit 26, afilter circuit 25 and a DC-to-DC buck converter 28. The power convertercircuit 20 is seen housed in housing 13 and advantageously provides afirst programmable DC output voltage at DC output terminal 16 and asecond programmable DC output voltage at terminal 18. Both of these DCoutput voltages may be generated as a function of both AC and DC inputvoltages.

In operation, the AC-to-DC converter 22 receives an AC signal via inputterminal 12 and provides a regulated DC output voltage at node N1.Similarly, the DC-to-DC booster converter 24 may receive a DC inputvoltage at its input via input terminal 14 and may also provide aregulated DC output voltage at node N1.

Input terminals 12 and 14 are integrated into a single common connector17 such that different power cords adapted to receive input power fromdifferent sources are received by the common connector 17. For instance,DC power from an airplane or car power source are wired to couple toinput 12 and AC source is wired to couple to input 14. In a selectedembodiment, the AC-to-DC converter 22 is adapted to generate a DC outputvoltage of between 15VDC and 24VDC in response to an AC input voltage atterminal 12 ranging between 90VAC and 265VAC. Likewise, the DC-to-DCbooster converter 24 is adapted to provide a DC output voltage which issubstantially similar to that of converter 22, but which is generated inresponse to a DC input voltage supplied at input terminal 14.Preferably, DC-to-DC booster converter 24 is adapted to receive avoltage in the range of between 11VDC and 16VDC. Advantageously,AC-to-DC conversion, via AC-to-DC converter 22, allows users of thepower converter 10 to power high-power mobile devices, such as a laptopcomputer wherever AC input power is available, such as in the home oroffice, for example. Conversely, the DC-to-DC booster converter 24 ofthe power converter 10 is capable of powering similar high-power devicesby stepping up most low amplitude DC input signals, such as those foundin automobile and/or airplane environments.

As shown, filter circuit 25 has its input tied to the respective outputsof the converter 22 and 24. In a preferred embodiment, the filtercircuit is adapted to provide a filtered DC output voltage at secondnode N2, which, thereafter, feeds output terminal 16, at an output powerof 75 watts, for example.

The single feedback circuit 26 is shown coupled to the output of filtercircuit 25 at node N2. In a preferred embodiment, the feedback 26circuit, through a single feedback loop, regulates the voltage level ofthe filtered DC output voltages generated by both converters 22 and 24.Additionally, the feedback circuit 26 is adapted to receive a removableprogramming module that allows mobile device users to provide aselectable DC output voltage at output 16 via node N2. The programmingmodule comprises a key 15 comprising a resistor, wherein differentassociated values of the resistor establish different associated DCoutput voltages at output 16. By allowing users to selectively changethe voltage level of the filtered DC output voltage, the power converter10 may be adapted to power a variety of different mobile electronicdevices, having different associated power requirements. Moreover, thepower converter's 10 programming module may also be adapted to providethe additional function of output current limiting.

The DC-to-DC buck converter 28 has its input coupled at node N2,providing a second DC output voltage that is then fed to output terminal18, having an output power of 10 watts, for example. Preferably, buckconverter 28 discreetly steps down the filtered DC voltage and producesa second DC output voltage at a separate output terminal 18. In aselected embodiment, the buck converter 28 steps down the filtered DCoutput voltage to a range of about 3VDC and 15VDC. Advantageously, thissecond DC output voltage generated by converter 28 is independent of,and substantially lower than the DC output voltage at terminal 16. Thisallows users of the present invention to power not only a high-powerperipheral, such as a laptop computer, but also, a second, low-powerperipheral, such as a cell phone, PDA, and the like. Moreover, thepresent invention allows for these peripherals to be poweredsimultaneously by a single converter, regardless if the input voltage isAC or DC. The buck converter 28 is physically detachable from the mainhousing 13 as shown in FIG. 1B, allowing different buck circuitsproviding different output voltages to be selectively attached tohousing 13 and tap the DC output voltage from output terminal 18.

Referring now to FIG. 2 there is shown a schematic diagram of the powerconverter circuit 20 of the dual input AC/DC power converter 10 asdepicted in FIG. 1 in accordance with an exemplary embodiment of thepresent invention. As described herein in greater detail, the powerconverter circuit 20, in a preferred embodiment, comprises threeseparate converters: AC-to-DC power converter 22, DC/DC boost converter24, and DC-to-DC buck converter 28.

AC-to-DC Converter

The AC-to-DC power converter 22 includes a true off line switcher whichis configured in a fly-back topology. Full-wave rectification of an ACinput signal, received at input terminal 12, occurs using a full-wavebridge rectifier BD1 and a filter capacitor C1, which creates a DCvoltage bus from which the switcher operates. Inductor L1 offersadditional EMI filtering of the AC signal after the signal has beenrectified through the full-wave bridge. The AC-to-DC converter 22 alsoincludes a main controller IC1 configured as a current mode pulse-widthmodulator (PWM). Main controller IC1 is also configured to have asingle-ended output with totem pole driver transistors coupled thereto.The AC-to-DC power converter 22 has a main power switch Q1 which drivesthe main transformer T1. In a preferred embodiment, the transformer T1,Schottky diode D11, and filter capacitors C24 and C25 combine to providethe DC output voltage at node N1.

As noted earlier, filter circuit 25 allows for additional filtering ofthe DC output voltage derived from node N1. The filter circuit 25 itselfcomprises inductor L3, capacitor C26 and transformer NF1.Advantageously, the filter circuit 25 produces a filtered DC outputvoltage at output 16 having less than 100 mv peak-to-peak noise andripple.

The feedback circuit 26, through a single feedback loop, is capable ofregulating the filtered DC output voltages provided by the converters 22and 24. The feedback circuit 26 is also adapted to be coupled to aremovable programming module having a key 15, comprising resistor R53.As such, the present invention allows users to selectively program theDC output voltage later received at output terminal 16. The feedbackcircuit 26 includes a photocoupler circuit comprising a pair ofphotocouplers PH1 and PH3 connected in series (i.e., stacked), eachbeing coupled to the outputs of operational amplifiers IC4-A and IC4-B.Advantageously, these photocouplers are arranged along the feedback loopof the feedback circuit 26. Additionally, the feedback circuit 26efficiently regulates the filtered DC output voltages generated by bothconverters 22 and 24 through a single feedback loop. In stacking thephoto-couplers, the present invention also allows the power converter 10to maintain proper input/output isolation between respective terminals12 and 14 and output terminal 16.

Preferably, the output current limiting function of converter 22 isaccomplished via integrated circuit IC4A, resistors R33, R37, R38, andR39 and programming resistor R54.

Over voltage protection of AC-to-DC converter 22 is achieved usingphotocoupler PH2 and zener diode ZD2. In a preferred embodiment, zenerdiode ZD2 is set at 25V such that when in avalanche mode it causes thetransistor side of photocoupler PH2 to bias transistor Q1 into the onstate. When it is the on state, transistor Q3 pulls low pin 1 ofintegrated controller IC1 and pulls the operating duty cycle of theintegrated controller towards 0%. This takes the DC output voltage to 0volts. Also, when transistor Q1 is on, transistor Q2 is also forced onwhich then forces these two transistors become latched. If transistorsQ1 and Q2 are latched, input power must be recycled in order for thepower converter 10 to be turned on again.

DC-to-DC Converter

The DC-to-DC converter 24 is configured in a boost topology and utilizesthe same kind of integrated controller, IC2, as used in converter 22. Inthe DC-to-DC converter 24, transistor Q8 acts as the main power switchand diode D6 as the main rectifier. Preferably, inductor L2 is adaptedto function as a power boost inductor, which is comprised of a toroidcore-type inductor. It should be understood that the cathode leads ofdiodes D11 and D8 are connected, forming an ORed configuration,requiring only one output filter. Advantageously, this eliminates theboard space needed for a second set of filters capacitors.

Like the AC-to-DC converter 22, the DC-to-DC converter 24 is alsodesigned to operate at a frequency of around 80 KHZ. For the AC-to-DCconverter 22, the operating frequency is set by resistor R13 andcapacitor C7. Likewise, the operating frequency of the DC-to-DCconverter 24 are set by resistor R28 and capacitor C28.

The DC-to-DC converter 24 includes an over-voltage protection circuitcomprising zener diode ZD2, resistor R23, R24, R48, transistor Q415, andsilicon-controlled rectifier SC1. Zener diode ZD2 sets the over-voltageprotection point (OVP) which is preferably set at 25VDC. Generally,there is no current flowing through resistor R48. If, however, whenzener diode ZD2 begins to conduct current, the drop across R48 issignificant enough to bias transistor Q6 on, pulling its collectorterminal high, and thereby turning silicon controlled rectifier SC1 on.When silicon control rectifier SC1 is on, it pulls pin 1 of theintegrated controller IC2 low. Thus, if pin 1 of integrated controllerIC2 is low, the output drivers thereof are forced to operate at a dutycycle of 0%, thereby producing a DC output voltage of 0 volts at pin 6.Advantageously, the silicon controlled rectifier SC1 functions as apower latch circuit that requires that input power be recycled in orderto turn on the power converter 10 if a voltage above 25VDC is detectedat node N1.

The temperature of the housing 13 of the power converter 10 is monitoredusing a thermistor NTC3. If, for example, there is a correspondingincrease in the temperature of the housing 13, it will result in adecrease in the resistive value of thermistor NTC3, thereby causingtransistor Q9 to turn on and pull low pin 1 of integrated circuit IC2 ofconverter 24. Moreover, this causes the photo-coupler PH2 to be biasedenough to activate a latch circuit comprising transistors Q1 and Q2 thatwill shutdown the power converter 22. In addition, the power converter's10 thermal protection feature is adapted to operate regardless ofwhether an AC or DC input voltage is being received at their respectiveinput terminals.

FIG. 3 shows a detailed schematic diagram of the DC-to-DC buck converter28 in accordance with the present invention. The buck converter 28 hasan integrated circuit controller IC1, similar to converters 22 and 24,which is adapted to generate an on-time duty cycle to power transistorswitch Q1. The operating frequency of controller IC1 is set by capacitorC6, which is coupled between pin 4 of IC1 and ground, and resistor R1,which is coupled between pins 4 and 8. In a selected embodiment, thediode D1 functions comprises a Schottky diode and functions as “catch”diode. Inductor L1 is a output power inductor and couples the gate ofpower transistor Q1 to V_(out). Fuse F1 is shown coupled between V_(in)and the drain terminal of power transistor Q1, and advantageouslyprovides current protection to buck-converter 28.

Furthermore, the input V_(in) of the buck converter 28 is coupled to theoutput of filter circuit 25 at node N2, wherein V_(in) receives thefiltered DC output voltage therefrom. In a preferred embodiment, thebuck converter 28 provides a second DC output voltage at V_(out),coupled to output terminal 18. Advantageously, the buck convert 28discreetly steps down the filtered DC output voltage and provides asecond DC output voltage at output terminal 18 which is independent of,and substantially lower than the DC output voltage at output terminal16. Likewise, the DC output voltage of the buck converter 28 enablesusers low-power peripherals, such as, a cell phones, a PDAs, and/orsimilar mobile devices. In a selected embodiment, the buck convert 28may also be adapted to provide a DC output voltage at output terminal 18ranging between 3VDC and 15VDC, selectively determined as a function ofthe chosen value of resistor R1 used in the particular buck converter28, with a total power delivery of 10 watts, for example. As previouslymentioned, the buck converter 28 may be housed in a separate, detachableprogram module that enables users to selectively program the DC outputvoltage at terminal 18 as a function of different associated buckconverter modules.

Though the invention has been described with respect to specificpreferred embodiments, many variations and modifications will becomeapparent to those skilled in the art upon reading the presentapplication. It is therefore the intention that the appended claims beinterpreted as broadly as possible in view of the prior art to includeall such variations and modifications.

What is claimed is:
 1. A power converter, comprising: a first circuitconverting an AC input voltage to a first predetermined DC outputvoltage; a second circuit converting a DC input voltage to a secondpredetermined DC output voltage; a third circuit receiving said firstand second predetermined DC voltages and, in response thereto, providinga selectable DC output voltage at a first output, wherein saidselectable DC output voltage is established as a function a removableprogram module; and a fourth circuit coupled to said first output andproviding a second DC output voltage at a second output, whereby saidsecond DC voltage output is independent of, and substantially lower thansaid selectable DC output voltage.
 2. The power converter of claim 1further comprising a fifth circuit comprising a filter circuit adaptedto filter said first and second predetermined DC output voltages andprovide a respective first and second filtered DC output voltage at acommon node.
 3. The power converter of claim 1 wherein said firstcircuit comprises a AC-to-DC flyback converter, wherein said AC-to-DCflyback converter is adapted to provide a DC output voltage of between15VDC and 24VDC.
 4. The power converter of claim 1 wherein said secondcircuit comprises a DC-to-DC boost converter, wherein said DC-to-DCboost converter is adapted to provide a DC output voltage of between15VDC and 24VDC.
 5. The power converter of claim 1 wherein said thirdcircuit includes a feedback circuit coupled to said first circuit andsaid second circuit, said feedback circuit regulating the first andsecond predetermined DC voltages generated by said first and secondcircuits.
 6. The power converter of claim 5 wherein said feedbackcircuit comprises a single loop.
 7. The power converter of claim 1wherein said fourth circuit comprises a DC-to-DC buck converterproviding said second DC output voltage, said DC-to-DC buck converterproviding said second DC output voltage of between 3VDC and 15VDC. 8.The power converter of claim 1 wherein said first and secondpredetermined DC output voltages are substantially the same and areprovided to a common node.
 9. The power converter of claim 1 whereinsaid first and second predetermined DC output voltages of saidrespective first and second circuit are established via said removableprogram module, wherein said removable program module comprises a keyadapted to be removably coupled to said power converter.
 10. The powerconverter of claim 1 wherein said removable program module comprises akey having a resistor, wherein said first and second DC output voltageare a function of the value of said resistor.
 11. The power converter ofclaim 10 wherein said key establishes an output voltage function. 12.The power converter of claim 10 wherein said key establishes an outputcurrent limiting function.
 13. The power converter of claim 1 whereinsaid first circuit is adapted to receive an AC input voltage having arange of 90VAC to 265VAC.
 14. The power converter of claim 1 whereinsaid second circuit is adapted to receive a DC input voltage having arange of 11VDC to 16VDC.
 15. The power converter of claim 1 wherein saidfirst and second predetermined DC output voltages are programmable as afunction of the program module.
 16. The power converter of claim 1wherein said fourth circuit comprises a second removable program module,wherein said second DC output voltage at said second output is afunction of said different associated second removable program modules.17. The power converter of claim 1 wherein said fifth circuit furtherincludes a protection circuit, said protection circuit provides anover-voltage protection function.
 18. The power converter of claim 1wherein the first circuit and the second circuit receive theirrespective AC input voltage and DC input voltages at a common singleconnector.